1. Field of the Invention
The present invention relates to an optical head device applicable to a magneto-optical or optical information recording and reproducing apparatus.
2. Related Background Art
An optical head of this type uses an objective lens for irradiating a laser beam condensed to approximately 1 .mu.m in diameter onto a surface of a disk-shaped recording medium, and a deflection mirror for deflecting the light beam to an optical path which guides the light beam from the semiconductor laser which serves as a light source to the objective lens. For example, as shown in FIGS. 1 and 2, the optical head device comprises an objective lens 6, an objective lens holding member 1 for holding the objective lens 6, adjusting means for finely moving the objective lens 6 along an optical axis of the objective lens and/or along a tracking direction for compensating for; and defocusing due to a plane vibration of a disk-shaped recording medium 17 and/or compensation for and change a positional error due to the eccentricity of the recording medium 17, and an optical system in optical head holding member (carriage) 4 to associate with the objective lens 6, a light source and a sensor through an optical path. The adjusting means comprises a focusing coil 8 and a tracking coil 9 arranged on an outer periphery of the objective lens holding member 1, permanent magnets 10a and 10b arranged to face the coils 8 and 9 and the optical head holding member 4, and electromagnetic yokes 11a and 11b. The optical system comprises a deflection mirror 12 as well as a beam splitter, a condenser lens, a photo-detector and a semiconductor laser (all of which are not shown). In the present embodiment, the elements other than the objective lens 6 and the deflection mirror 12 are arranged on a fixed base which is separate from the optical head holding member 4 and they are linked to the deflection mirror 12 through an optical window. A cover 13 having an opening 21 formed at a portion facing the objective lens 6 is attached to the optical head holding member 4 and it covers an upper space between the objective lens 6 and the deflection mirror 12. Sliding bearing holes 14 and 15 for moving the optical head holding member 4 are formed in the optical head holding member 4 along the tracking direction 19. A guide rail (not shown) is inserted into the holes 14 and 15.
Such a prior art optical head device has the following problem. When the disk-shaped recording medium 17 is rotated in a direction 18 for recording or reproducing information, a negative pressure which sucks air into the opening 21 is created. External air flows into the optical head holding member 4 through the optical path window 16 or the bearing holes 14 and 15 and further into the cover 13 through the optical path window 22, and dust is carried in thereby. The dust is deposited the optical elements in the optical path. When dust deposits on the surface of the deflection mirror 12 or the objective lens 6, a light intensity to the recording medium in the recording or reproducing mode and a light intensity of the reflected light are adversely affected and correct writing and reading are impeded.